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Work

Work. CHAPTER 2. KEY QUESTION: What is “work” and how does it occur? Main Points: Simple machines are an important part of many systems and subsystems. Many types of forces affect our everyday lives. We use simple machines and other systems to make work easier to do.

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Work

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  1. Work CHAPTER 2 KEY QUESTION:What is “work” and how does it occur? Main Points: Simple machines are an important part of many systems and subsystems. Many types of forces affect our everyday lives. We use simple machines and other systems to make work easier to do. The mechanical advantage of a simple machine and the amount of work done by a simple machine can be calculated. Experimentation skills can be used to determine the effectiveness of simple machines. Making work easier to do is not the same as doing less work. There are words that have a more specific meaning in science class than they do in everyday life (ex: work).

  2. VOCABULARY • simple machine: a device that requires a single force to work • Fulcrum: the pivot point of a lever • load arm: the part of a lever that extends from the fulcrum to the mass being moved • effort arm: the part of a lever that extends from the fulcrum to where the force is applied • input force: the effort force applied to the lever • output force: the force the lever applies to the load • load force: the force that the input force has to overcome in order to cause movement

  3. 2.1 Physical Systems: Simple Machines • A simple machineis a device, composed of only one or two parts, that requires a single force to work. • Simple machines fall into two main groups: those related to the inclined plane and those related to the lever . • Simple machines can change the size and the direction of the input force, and transfer the input force to another part of the machine.

  4. 2.1 Physical Systems: Simple Machines • One group of simple machines includes the inclined plane, the wedge, and the screw. • Ramps and staircases are examples of an inclined plane. • A wedge is a modified inclined plane. A knife is an example of a wedge. • A screw is an inclined plane that has been cut into a central core.

  5. VOCABULARY • Magnitude the amount of force • newton (N) the unit used to measure forces (N) • Friction is the force that resists motion between two objects in contact with each other • static friction the force that holds a motionless object where it is • sliding friction the force that acts like a brake when one surface slides over another surface • Lubricant a substance that reduces friction and causes surfaces to slide more easily VITAL SCIENCE

  6. Now can you… • • identify forces that can be observed in everyday life • • explain how forces are represented in a diagram • • describe the relationship between mass, weight, and gravity • • recognize that friction is a force that resists motion • CYL 1,2,3 pg. 39 • BONUS Activity (Completely optional BUT worth extra credit if completed). Write a one-page report on how friction is caused by electromagnetic interactions.

  7. VOCABULARY • mechanical advantage(MA): Is how we measure how much a given machine helps us do work (comparison of output force to input force for a given machine). MA = Output Force Input Force • Work: The result when a force moves an object (UNITS = Nm or Joules (J) WORK = Force Applied in newtons (N) X Distance moved in meters (m) WORK = N x m • Energy: The ability to do work.

  8. 2.3 Mechanical Advantage • Simple machines often make physical tasks easier to perform (such as using a hammer to remove a nail) because they can turn a small input force into a larger output force. • Mechanical advantage (MA) is the ratio of the output force to the input force (i.e., the output force divided by the input force).

  9. 2.3 Mechanical Advantage • The ideal mechanical advantageis what the mechanical advantage would be if all the input force could be converted into an output force. Actual mechanical advantageis the mechanical advantage that actually occurs. • To calculate the actual mechanical advantage we must measure the actual forces involved.

  10. 2. The Scientific Meaning of Work • Workis done only when a force applied to an object causes the object to move a distance parallel to the force. • Energy isthe ability to apply a force to move an object a distance.(i.e. you have energy because you have the ability to move an object.) • Although energy is always consumed when work is done, not all of the energy consumed is turned into useful work. Some is turned into useless heat, for example. • Energy, like work, is measured in joules.

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